A thermostat valve is installed in the cooling system of an automobile engine so that when the coolant is cold, such as just after the engine is started, the coolant is cut off from the radiator and circulated into the engine water jacket through the water pump, and when the coolant is hot, the coolant is supplied to the radiator and circulated to the engine after the coolant has been cooled.
Conventionally, a variety of different structures have been proposed for this type of thermostat valve. For example, a thermostat valve as disclosed in Patent Document 1 that is installed on the discharge side of the engine water jacket and controls the discharge of coolant is known. This thermostat valve uses a configuration in which the valve stem is closed in a direction that goes against the flow of coolant, onto a valve seat formed in the frame to simplify the structure of the valve as a whole, make the valve more compact, and improve valve performance.
This configuration is dictated by the fact that if, contrary to the foregoing description, the valve stem were to be closed with the flow of coolant, then the frame and other structural components would have to be configured to enable the valve stem to open against the flow and the pressure of the coolant when the valve opens, thereby unavoidably making the overall structure larger and more complicated. Moreover, a valve that operates this way tends to exhibit a delay in the movement of the valve stem, although this sort of problem is solvable.